The Web's Most Illogical Arguments
That information came from Wikipedia, and we all know Wikipedia can't be trusted.
Like the ad hominem approach, the above argument ignores the content of a statement and puts all of its energy into attacking the source. We call this a genetic fallacy because it suggests that information may automatically be untrue simply because of where or who it came from. Of course, that's baloney. To prove that a given statement is either factually wrong or illogical, you have to address the content of the statement itself.
No True Scotsman
Mike: No Linux user would say something like that.
Billy: I'm a Linux user.
Mike: No real Linux user would say something like that.
The No True Scotsman gambit is cheesy bit of rationalization that draws an imaginary distinction between one kind of thing and a nonexistent "true" version of that thing, usually as a way of avoiding admitting a mistake.
In the example above, Mike modifies his original false statement with a qualifying word ("real") that makes the assertion subjective rather than objective. Whereas the claim "No Linux user would say something like that" is disprovable by a single exception, the claim "No real Linux user would say something like that" allows Mike to avoid acknowledging that Billy counts as such an exception: In fact, Mike's revised wording amounts to saying that by contradicting the original assertion, Billy automatically disqualifies himself from being a "real" Linux user. In online forums, many people skip the first step and jump straight to the No True Scotsman fallacy. It saves time, but it's still wrong.
The Straw Man
Dan: Netbooks can be easier to use than full-size laptops when you're traveling, because they're lighter and fit better on an airplane tray table.
Jimbo: You're saying that netbooks are better than laptops, which is stupid because laptops have faster processors, bigger screens, and better keyboards. You're an idiot.
Want an opponent who's easy to beat up? Build yourself a straw man--he doesn't even have a brain. The straw man fallacy is irritating because it misrepresents and trivializes the opposing view. In the example above, Jimbo alters Dan's argument to make it patently false, and then attacks the weaker argument instead of addressing what Dan actually said. Jimbo is ignoring the fact that Dan was talking a specific circumstance in which his statement might be true. Jimbo is a jerk.
Argument From Ignorance
I've never seen any evidence that disk defragmentation speeds up PCs, so it's clearly a waste of time.
If you don't know something, it's hard to draw a reliable conclusion about it. This is the core weakness of the argument from ignorance. In the above example, the arguer draws a conclusion based on a lack of evidence--which is pretty much the opposite of rational inference. Not only is this guy reaching a conclusion based on not having seen something, but it's unclear whether he ever tried to gather the information in the first place. It's the same fallacy as saying "I've never seen duck-billed platypus, so there are no duck-billed platypuses." Of course, your personal experience of something is by no means irrelevant to your assessment of it: Never having seen a Gorn except on Star Trek is a data point that you can legitimately consider in assessing whether Gorns exist. But your personal experience isn't the sole arbiter of what is real. As a matter of logic, we can't use our own ignorance (or nonexperience) as dispositive proof that an assertion is true (or false).
Almost everybody uses Windows. It's clearly the best OS around.
Also known as an appeal to popularity, this fallacy equates popularity with value. By this reasoning, the Big Mac is the best hamburger on earth and Reader's Digest is the best magazine. It's possible for a best-selling product to be the highest-quality one as well, but popularity doesn't automatically mean excellence. If you want to prove that your favorite operating system, phone, or other media player is better than the competition, try talking about its features.
The Hot Hand
Apple has released a lot of great products lately. Its next Apple gadget is bound to be great.
Depending on who you ask, the hot-hand fallacy gets its name from the sports world or from the gambling world, where players tend to believe that a series of back-to-back wins indicates a "hot streak." There's nothing fallacious about acknowledging a run of successes, but a past win does not guarantee a future win, any more than a run of ten heads on consecutive flips of a normal, balanced coin makes heads (or tails) more likely on the next flip.
The above example from the tech world is a fallacy because it asserts that a particular future outcome is a certainty, based entirely on past performance, without offering any substantive support for the expected result. But a given product succeeds or fails (for the most part) on its own merits. And while having a talented design team undoubtedly strengthens a company's chances of putting together something great, the argument used in this example doesn't focus on that legitimate consideration at all.
Like every other decades-old business, Apple has had some misses as well as hits. The tendency to ignore the strikeouts and remember only the home runs is an example of a well-known psychological effect called confirmation bias.